# stats

if you randomly answer a t/f test and want to figure the possibililty of gettng at least an 80......how do you start and then once you have done this, what if you want to try it 4 more times? HELP

Let N be the number of questions. You are asking for the probability of getting N/5 or fewer wrong by randomly guessing.

Assume N>> 1 and use an error-function approximation for the number of questions answered correctly. The mean will be N/2 and the standard deviation will be sqrt[N*p*(1-p)] = (1/2)sqrtN, since p = 1/2 is the probability of getting each one right.
Inegrate the probability of correct answers from 0.8 N to N, which you can treat as infinity when N is very large.

The larger the value of N, the less likely you will be to get 80% right.

For N=25, I get a standard deviation of 2.5 about a mean of 12.5, and the probability of getting 20 or more right will be 0.0013. It becomes a much lower probability of N = 100. You need to use an error function table for this sort of problem.

1. 👍 0
2. 👎 0
3. 👁 169

## Similar Questions

1. ### math

Test scores on a university admissions test are normally distributed, with a mean of 500 and a standard deviation of 100. a. What is the probability that a randomly selected applicant scores between 425 and 575? b. What is the

asked by ananya on April 15, 2015
2. ### Probablity

Samir had prepared the problem tests for Stages 1 to 5 of Geometry and Combinatorics for next week but forgot to label which test was for which stage. Since Samir didn't label them, the computer assigned them labels 1 through 5

asked by Mathslover on May 14, 2013
3. ### statistics

LSAT test scores are normally distributed with a mean of 510 and a standard deviation of 110. Find the probability that a randomly chosen test-taker will score between 300 and 580. (Round your answer to four decimal places.)

asked by Anonymous on November 21, 2012
4. ### statistics

LSAT test scores are normally distributed with a mean of 490 and a standard deviation of 110. Find the probability that a randomly chosen test-taker will score between 320 and 600. (Round your answer to four decimal places.)

asked by jack on April 16, 2013
5. ### Statistics

Twenty (20) students randomly assigned to an experimental group are studying for a test while listening to classical music. Thirty (30) students randomly assigned to a control group are studying for the same test in complete

asked by Jennifer on July 31, 2011
1. ### statistics

Twenty (20) students randomly assigned to an experimental group are studying for a test while listening to classical music. Thirty (30) students randomly assigned to a Control group are studying for the same test in complete

asked by Cyn on May 3, 2011
2. ### statistics and probability

n a written test given to a large class comprising 42 students, the test scores were found to be normally distributed with a mean of 78 and a standard deviation of 7. A minimum score of 60 was needed to pass the test. A score of

asked by faye on February 14, 2017

16-To test the hypothesis H0 : ì = 100 against H1 : ì > 100, a statistics practioner randomly sampled T observations and found the mean x = 106 and the standard deviation sx = 35. The value of the test statistic is equal to (1)

asked by Judy and group on April 1, 2010